The molecular basis of melanism and mimicry in a swallowtail butterfly

Abstract

Melanism in Lepidoptera, either industrial or in mimicry, is one of the most commonly cited examples of natural selection [1] [2]. Despite extensive studies of the frequency and maintenance of melanic genes in insect populations [1] [2], there has been little work on the underlying molecular mechanisms. Nowhere is butterfly melanism more striking than in the Eastern Tiger Swallowtail (Papilio glaucus) of North America [3] [4] [5]. In this species, females can be either yellow (wild type) or black (melanic). The melanic form is a Batesian mimic of the distasteful Pipevine Swallowtail (Battus philenor), which is also black in overall color. Melanism in P. glaucus is controlled by a single Y-linked (female) black gene [6]. Melanic females, therefore, always have melanic daughters. Black melanin replaces the background yellow in melanic females. Here, we show that the key enzyme involved is N-beta-alanyl-dopamine-synthase (BAS), which shunts dopamine from the melanin pathway into the production of the yellow color pigment papiliochrome and also provides products for cuticle sclerotization. In melanic females, this enzyme is suppressed, leading to abnormal melanization of a formerly yellow area, and wing scale maturation is also delayed in the same area. This raises the possibility that either reduced BAS activity itself is preventing scale sclerotization (maturation) or, in contrast, that the delay in scale maturation precludes expression of BAS at the correct stage. Together, these data show how changes in expression of a single gene product could result in multiple wing color phenotypes. The implications for the genetic control of mimicry in other Lepidoptera are discussed.

Multiple, recurring origins of aposematism and diet specialization in poison frogs

“…1). Such low genetic divergence is not necessarily inconsistent with extreme color divergence, because color pattern in some model organisms is controlled by very few genes (35). Nonetheless, the low genetic divergence suggests the microevolutionary lability of defensive signals and toxicity in these frogs.…”

yellow and ebony Are the Responsible Genes for the Larval Color Mutants of the Silkworm Bombyx mori

“…In Lepidoptera, the Ebony protein is involved in the production of yellow papiliochrome in Papilio glaucus adult wing (Koch et al 2000) and reddish-brown pigments in P. xuthus larval body markings (Futahashi and Fujiwara 2005). The activity of Ebony is concerned with light pigmentation in both cases.…”

A Pathway Analysis of Melanin Patterning in a Hemimetabolous Insect

“…In those studies, this specific black pattern becomes lighter in yellow RNAi individuals, whereas ebony RNAi has no effect on the flanking nonblack subregions (Tomoyasu et al 2009;Arakane et al 2010). The erasing mode may be evidenced in the butterfly Papilio, where the default fully melanized forewing was observed in ebony mutant adults (Koch et al 2000). Another example is the depletion of ebony or black in Tribolium, which results in the general blackening of the whole body Tomoyasu et al 2009).…”